The present invention relates to a control cable, and more particularly to a control cable excellent in load efficiency, and the inner cable of which being able to be smoothly operated for a long period of time.
A control cable fundamentally comprises a flexible conduit and a flexible inner cable which is inserted into the conduit so as to be freely slidden in and out, and is a means for remotely controlling a slave connected with the end of the inner cable by applying a pulling operation, a pushing and pulling operation or the combination thereof to another end of the inner cable. The control cable has been conventionally used in order to operate a transmission used in automobiles, autobicycles, bicycles and the like, a brake, a clutch, a speedmeter, and the like.
The inner cable usually comprises a stranded wire produced by twisting plural metallic wires or a stranded wire of which surroundings are coated with a synthetic resin or reinforced by twisting flat steel wires around the stranded wire. The conduit comprises, for instance, a coiled spring produced by winding one or plural flat steel wires or round steel wires in abutting convolutions and an outer coat made of a synthetic resin which covers the outside surface of the coiled spring.
However, in such a control cable, frictional resistance increases when the conduit is directly contacted with the inner cable. Therefore, in some cases, as diclosed in Japanese Patent Unexamined Publication No. 231009/1985, a flexible tubular liner made of a synthetic resin is formed on the inside surface of the conduit. As a material used in the liner, for instance, a synthetic resin such as polyethylene, polyoxymethylene, polybutylene terephthalate or polytetrafluoroethylene is used.
Also, a synthetic resin coating (hereinafter referred to as inner coat) is set on the outer surroundings of the inner cable. As a material for the inner coat, for instance, Teflon, 11-nylon and the like are used.
However, in such a control cable having the above-mentioned liner and inner coat, in order to diminish the sliding resistance between the liner and the inner cable, there is a necessity to use a synthetic oil such as silicone oil or olefin oil, a mineral oil, a grease of which basic ingredient is the above oil, or a lubricant such as oil or grease in which an antioxidant, a corrosion inhibitor, an extreme pressure additives and the like are added, between the inner cable and the conduit in consideration of the affection of the load efficiency [(given load/operation load).times.100].
However, there are several problems, in the control cable in which a lubricant is used, such as difficulty of operation for coating because dispersion of the load efficiency of products is caused by the unevenness of a coating, rubbishes and dusts are easily adhered to the lubricant when applying the lubricant to the control cable, and drip and the like are generated.
Also, the durability of the above-mentioned control cable largely depends upon the lubricant. For instance, in case the shortage of lubricants is generated due to the long period use of the control cable, there are some problems that the liner is thoroughly worn down and the operationability of the control cable is excessively lowered, and the like.
The object of the present invention is to delete the above-mentioned disadvantages of conventional control cables and to provide a control cable which does not necessitate a lubricant to avoid a complex coating operation and which can be used with smooth sliding operation of the inner cable for a long period of time.